Method of manufacturing metal embossed plate

ABSTRACT

First corrugated portions in a first direction are sequentially formed by die-pressing a raw metal plate. Second corrugated portions formed in a second direction intersecting the first direction are sequentially formed by die-pressing a primary formed plate having the first corrugated portions using elongate projections, so that each of the second corrugated portion has a half-height and a pitch larger than those of each of the first corrugated portion. Third corrugated portions formed approximately in the first direction are sequentially formed by die-pressing a secondary formed plate having the second corrugated portions using elongate projections, so that each of the third corrugated portions has a half-height and a pitch larger than those of the first corrugated portion.

BACKGROUND OF THE INVENTION (1) Field of the Invention

The present invention relates to a metal embossed plate that can suitably be used as a covering member for covering an exhaust part of a road vehicle, an exhaust part covering member of a road vehicle using the metal embossed plate, and a method of manufacturing the metal embossed plate.

(2) Description of Related Art

Fuel consumption rises as a weight of a road vehicle increases. Requirements for fuel consumption are becoming severer year by year along with the requirements for CO₂ emission. Reduction in the weight of the road vehicle is definitely needed. Meanwhile, road vehicles are becoming heavier for various reasons, such as requirements of crash safety standards for higher strength against offset crash and the increase in the number of devices installed for improving comfort of a road vehicle. To reduce a weight of a part of a road vehicle, use of aluminum alloy materials (aluminum materials), which have high advantages in integrating parts, lightweight, high strength, and corrosion resistance are expected to expand.

The exhaust system of a road vehicle (car) is required to be designed in an environmentally friendly manner, so priority is placed on requirements for weight reduction, heat insulation, and compactness.

For example, as for a cover that covers an exhaust manifold, an aluminum alloy cover is becoming the mainstream for weight reduction instead of an iron plate cover. In addition, a cover that is shaped to suitably fit to an exhaust manifold and a full-hooding cover that entirely covers the exhaust manifold are now used in order to provide higher heat insulation to achieve improved catalyst efficiency. As exhaust manifolds are made more compact, a shape of the cover is required to be deeper, which makes it more difficult to form by deep-drawing.

To meet such requirements, for example, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2001-504393 (Patent Literature 1) discloses a heat shield panel made of an aluminum alloy metal sheet having a plurality of approximately parallel and upright ridges, where the adjacent ridges have therebetween a groove having an inner bent side wall, the width of each ridge changes along the longitudinal direction of the groove by a certain pitch, the height of each ridge changes along the longitudinal direction and reaches the maximum at the narrowest ridge section, the depth of the groove changes along the longitudinal direction and reaches the maximum at the narrowest ridge section.

Furthermore, Japanese Patent No. 5705402 (Patent Literature 2) discloses a method of manufacturing an aluminum formed plate. In the method, an aluminum plate is passed through a pair of gear-shaped first corrugating rolls to form first corrugated projections, and then the aluminum plate is passed through a pair of gear-shaped second corrugating rolls in the direction perpendicular to the longitudinal direction of the first corrugated projections to form second corrugated projections. By this method, the ridge lines of the first corrugated projections and the ridge lines of the second corrugated projections form a lattice pattern. The aluminum formed plate thus formed can suitably be used as a shielding cover disposed over a heat generating part such as an exhaust pipe or an engine of a road vehicle.

Furthermore, International Publication No. 2013/046326 (Patent Literature 3) discloses a method of manufacturing a multiply-corrugated member. In the method, a thin plate is sandwiched between a pair of corrugating rolls to form a corrugated thin plate, and a corrugating process is performed a plurality of times on the corrugated thin plate in a manner that the direction of the corrugating process intersects the direction of the immediately preceding corrugating process, where the corrugating rolls can be changed for each corrugating process by a switching unit that switches corrugating rolls. In addition, Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2016-505388 (Patent Literature 4) and Japanese Unexamined Patent Application Publication No. 59-215219 (Patent Literature 5) disclose processing methods in which a raw metal plate is passed only once between a pair of corrugating rolls to undergoes a corrugating process.

In Japanese Examined Patent Publication No. 48-43414 (Patent Literature 6), a method of forming a single-type corrugated portion is proposed. In the method, a corrugating process is sequentially performed on a raw metal plate by die-pressing using elongate projections provided in a pair of dies capable of approaching and separating from each other.

SUMMARY OF THE INVENTION Problem to be Solved by the Invention

A metal sheet described in Patent Literature 1 easily stretches in a width direction of a ridge but not in a longitudinal direction of the ridge. This low stretch property in the longitudinal direction disadvantageously causes the reduction in the critical draw ratio. For this reason, the metal sheet cannot be drawn into a three-dimensional shape that suitably fits to a certain shape of an exhaust manifold, which causes failure to meet the requirements from road vehicle manufacturers and decrease in yield ratio resulting in high product cost. Moreover, the metal sheet described in Patent Literature 1 is formed of two overlapped plates joined by portions mechanically clinched by an inner-bent side walls, where the mechanically clinched portions are disposed on an entire surface of the metal sheet. These mechanically clinched portions may have an adverse effect on forming of a three-dimensional shape close to the shape of the exhaust manifold.

In an aluminum formed plate manufactured by the methods disclosed in Patent Literatures 2 and 3, convex portions and concave portions are created so that the ridge lines of the sinusoidal first corrugated projections and the ridge lines of the sinusoidal second corrugated projections form a lattice pattern. This result in the elongation percentage in the first direction being closer to the elongation percentage in the second direction in the aluminum formed plate than the metal sheet disclosed in Patent Literature 1, which raises the critical draw ratio and increases a range of design that can be formed by deep-drawing.

The methods in which corrugated portions are formed by passing a raw metal plate between a pair of corrugating rolls as described in Patent Literatures 2 and 3 have disadvantages such that: the corrugating rolls have a limited range of applicable design, namely, the corrugating rolls have to be redesigned if the half-height and the pitch of the corrugated portion are changed due to redesign of a product; if the corrugated portion is set to have a large half-height and a large pitch, expensive corrugating rolls having large diameters are necessary, causing the equipment cost to increase; and the half-height of the corrugated projection is determined by the tooth height of the corrugating roll. A large tooth height causes a large residual strain in the formed plate, causing the risk of cracking to increase, and a small tooth height results in the formed plate having a small total thickness that results in insufficient rigidity. Although the thickness of the raw metal plate may be increased to raise the rigidity of the formed plate, a larger thickness disadvantageously increases weight.

To improve combustion efficiency as much as possible, forming a covering member for an exhaust manifold with stainless steel, which has a thermal conductivity smaller than that of an aluminum alloy, is proposed. Such an idea, however, has not been put into practice because it is difficult, for forming the covering member to use the stainless steel that has smaller elongation percentage than aluminum alloy, by a conventional forming method without further improvement.

An object of the present invention is to provide a method of manufacturing a metal embossed plate that has sufficient strength and rigidity, a wide range of design formed by deep-drawing, and small residual strain, by adopting a raw metal plate that has as small a thickness as possible to reduce a weight of the metal embossed plate.

Means to Solve the Problem

The present invention includes the following inventions.

(1) A method of manufacturing a metal embossed plate including sequentially forming a plurality of first corrugated portions in a first direction by die-pressing a raw metal plate; sequentially forming a plurality of second corrugated portions in a second direction intersecting the first direction by die-pressing a primary formed plate having the first corrugated portions, each of the plurality of second corrugated portions having a half-height and a pitch larger than a half-height and a pitch of each of the first corrugated portions, and the die-pressing being performed using an elongate projection provided on at least one of a pair of dies capable of approaching and separating from each other; and sequentially forming a plurality of third corrugated portions approximately in the first direction by die-pressing a secondary formed plate having the second corrugated portions, each of the plurality of third corrugated portions having a half-height and a pitch larger than the half-height and the pitch of the first corrugated portion, the die-pressing being performed using an elongate projection provided on at least one of a pair of dies capable of approaching and separating from each other.

In this manufacturing method, the first corrugated portions each having the small half-height are sequentially formed by die-pressing the raw metal plate between a pair of gear-shaped corrugating rolls or by die-pressing the raw metal plate with the elongate projection. Since the first corrugated portion has a smaller half-height than the second corrugated portion and the third corrugated portion, residual strain in the raw metal plate can be reduced.

Meanwhile, the second corrugated portion and the third corrugated portion each having a larger half-height than the first corrugated portion are sequentially formed by die-pressing the primary formed plate or the secondary formed plate with the elongate projection. The corrugated portions can thus be formed on the metal embossed plate without difficulty.

The rigidity of the metal embossed plate can be improved by increasing the total thickness of the metal embossed plate while minimizing the residual strain throughout the metal embossed plate. Accordingly, the metal embossed plate having high rigidity can be obtained from a very thin raw metal plate. In addition, the second corrugated portion and the third corrugated portion each having a large half-height are formed on the metal embossed plate, allowing elongation percentages to be high in the first direction and the second direction. Accordingly, a range of designing a product that can be formed by deep-drawing can be broadened. Therefore, not just only an aluminum alloy plate but a stainless steel plate can be deep-drawn without difficulty, and a covering member having a shape that suitably fits to the shape of an exhaust part member of a road vehicle, such as an exhaust manifold, can easily be manufactured.

(2) The method of manufacturing a metal embossed plate according to (1), in which the first direction and the second direction are approximately orthogonal. With this manufacturing method, the elongation percentage is evenly distributed in the metal embossed plate. (3) The method of manufacturing a metal embossed plate according to (1) or (2), in which the half-height and the pitch of the second corrugated portion are set approximately same as the half-height and the pitch of the third corrugated portion, respectively. With this manufacturing method, the elongation percentage is evenly distributed in the metal embossed plate. In the specification, the half-height of the first corrugated portion means half the distance between the highest portion and the lowest portion of the corrugation of the primary formed plate, namely a half the total thickness of the primary formed plate with the first corrugated portion being formed on the raw metal plate. The half-height of the second corrugated portion means half the distance between the highest portion and the lowest portion of the corrugation of the secondary formed plate, namely a half the total thickness of the secondary formed plate with the first corrugated portion and the second corrugated portion being formed on the raw metal plate. The half-height of the third corrugated portion means half the distance between the highest portion and the lowest portion of the metal embossed plate, namely a half the total thickness of the metal embossed plate with the first corrugated portion, the second corrugated portion, and the third corrugated portion being formed on the raw metal plate. (4) The method of manufacturing a metal embossed plate according to any one of (1) to (3), in which the half-height of the third corrugated portion is 2 to 4 times the half-height of the first corrugated portion, and the pitch of the third corrugated portion is 2.14 to 5.5 times the pitch of the first corrugated portion. The half-height of the third corrugated portion is preferably two or more times of the half-height of the first corrugated portion to improve formability (elongation) in the second direction but up to four times the half-height of the first corrugated portion to reduce the residual strain in the first corrugated portion that is formed between the top and the bottom of the third corrugated portion and is deformed to accumulate residual strain by forming of the third corrugated portion. In addition, the pitch of the third corrugated portion is preferably 2.14 times or more the pitch of the first corrugated portion with two or more first corrugated portions provided between the adjacent bottom and top of the third corrugated portion to improve formability (elongation) in the second direction but up to 5.5 times the pitch of the first corrugated portion so that the bending rigidity in the second direction per unit length will not be too small due to a large pitch of the third corrugated portion, and thus sufficient bending rigidity is secured. (5) The method of manufacturing a metal embossed plate according to any one of (1) to (4), in which a stainless steel plate is used as the raw metal plate. Stainless steel has a smaller elongation percentage than aluminum alloy, but the corrugated portion can easily be formed on the metal embossed plate by forming the second corrugated portion and the third corrugated portion by die-pressing using the elongate projection as in the present invention. Moreover, stainless steel, which has smaller thermal conductivity than aluminum alloy, can meet customer's needs regarding heat insulation. (6) The method of manufacturing a metal embossed plate according to any one of claims (1) to (5), in which any one of the first corrugated portion, the second corrugated portion, and the third corrugated portion is die-pressed by a forming die having a surface that is treated with surface treatment by which dry lubricity of the surface increases. (7) The method of manufacturing a metal embossed plate according to any one of (1) to (6), in which the first corrugated portions are sequentially formed by die-pressing with a pair of gear-shaped corrugating rolls. In this case, productivity of the metal embossed plate can be improved by forming the first corrugated portion using the corrugating rolls. In addition, since the half-height and the pitch of the first corrugated portion are smaller than the second corrugated portion and the third corrugated portion, residual strain can be minimized even when the first corrugated portion is formed by die-pressing by a pair of corrugating rolls. By combining forming of the first corrugated portion using the corrugating rolls and forming of the second corrugated portion and the third corrugated portion by die-pressing using the elongate projection provided at least on either one of a pair of dies capable of approaching and separating from each other with the half-heights and the pitches of the second corrugated portion and the third corrugated portion being set larger than the half-height and the pitch of the first corrugated portion, respectively, productivity of the metal embossed plate can be improved with the second corrugated portion and the third corrugated portion, which have larger half-heights and pitches than the first corrugated portion. In addition, such second corrugated portion and the third corrugated portion can be formed easily while minimizing the residual strain in the metal embossed plate. (8) The method of manufacturing a metal embossed plate according to any one of claims (1) to (7), in which at least one of the second corrugated portion and the third corrugated portion is die-pressed multiple times to have depth that increases in a stepwise manner. With such a method, residual strain can further effectively be prevented in the corrugating process of forming the second corrugated portion and the third corrugated portion. (9) The method of manufacturing a metal embossed plate according to any one of (1) to (8), in which only three types of corrugated portions which are the first corrugated portion, the second corrugated portion, and the third corrugated portion are sequentially formed on the raw metal plate.

According to the method of manufacturing a metal embossed plate, a metal embossed plate that has sufficient strength and rigidity, a wide range of design formed by deep-drawing, and small residual strain, can be provided by adopting a raw metal plate that has as small a thickness as possible to reduce a weight of the metal embossed plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a metal embossed plate;

FIG. 2 is a view taken in a direction indicated by an arrow A in FIG. 1;

FIG. 3 is a view taken in a direction indicated by an arrow B in FIG. 1;

FIG. 4 is an explanatory view of a method of manufacturing a primary formed plate;

FIG. 5 is a front view of the primary formed plate and a first forming die;

FIG. 6 is an explanatory view of a method of manufacturing a secondary formed plate;

FIG. 7 is a front view of the secondary formed plate and a second forming die;

FIG. 8 is a view of the formed plate illustrated in FIG. 6 taken in a direction indicated by an arrow A;

FIG. 9 is a view of the formed plate illustrated in FIG. 6 taken in a direction indicated by an arrow B;

FIG. 10 is an explanatory view of a method of manufacturing a metal embossed plate;

FIG. 11 is a front view of the metal embossed plate and a third forming die;

FIG. 12 is a cross sectional view of a raw metal plate;

FIG. 13 is a perspective view of a first forming die of another configuration;

FIG. 14 is a perspective view of a first forming die of still another configuration;

FIG. 15 is a front view of a second forming die of another configuration; and

FIG. 16 is a perspective view of a noise insulating cover manufactured from a metal embossed plate and an exhaust part of an engine.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of the present invention will now be described with reference to the drawings.

As illustrated in FIGS. 1 to 3, a metal embossed plate 10 manufactured by a manufacturing method of the present invention has, on the entire plate, corrugations including combination of a plurality of first corrugated portions 11 formed in a first direction X, a plurality of second corrugated portions 12 formed in a second direction Y approximately orthogonal to the first direction X with a half-height and a pitch longer than those of the first corrugated portions 11, and a plurality of third corrugated portions 13 approximately in the first direction X. Curved lines a and b in the drawings are explanatory auxiliary lines drawn to show high portions and low portions of the corrugated portion.

The method of manufacturing the metal embossed plate 10 includes a first corrugating step illustrated in FIGS. 4 and 5 in which a flat raw metal plate 15 is die-pressed to sequentially form a plurality of first corrugated portions 11 in a first direction X, a second corrugating step illustrated in FIGS. 6 and 7 in which a primary formed plate 16 having the first corrugated portions 11 is die-pressed using elongate projections 33 and 37 to sequentially form a plurality of second corrugated portions 12 in a second direction Y intersecting the first direction X so that a half-height and a pitch become larger than those of the first corrugated portion 11, and a third corrugating step illustrated in FIGS. 10 and 11 in which a secondary formed plate 17 having the second corrugated portions 12 is die-pressed using elongate projections 43 and 47 to sequentially form a plurality of third corrugated portions 13 approximately in the first direction X so that a half-height and a pitch larger become than those of the first corrugated portion 11.

As the raw metal plate 15, any press-formable metal material, such as aluminum alloy, iron, and stainless steel, can be used. In the case of manufacturing covering members 51 and 52 from the metal embossed plate 10 to cover an exhaust manifold 50 of a road vehicle engine as illustrated in FIG. 16, an aluminum alloy plate is used as the raw metal plate 15 to reduce the weight of the vehicle body or a stainless steel plate is used as the raw metal plate 15 to provide high heat insulation to improve engine performance. The raw metal plate 15 may be a single metal plate or a multi-plate raw metal plate that is a plurality of metal plates integrated by, for example, spot welding. As illustrated in FIG. 12, for example, a raw metal plate 15A having a multi-plate structure of two stacked metal plates 52 and 53 integrated by spot welding may be used. Although the raw metal plate having a multi-plate structure may be composed of stacked metal plates of the same thickness, it is preferable to use the metal plates 52 and 53 having different thicknesses as illustrated in FIG. 12 so that the difference in resonance frequencies of the metal plates 52 and 53 improves vibration damping performance of the metal embossed plate.

The raw metal plate 15 may be a flat plate having a thickness t of 0.1 mm to 0.5 mm. The raw metal plate 15 may have any dimension in the first direction X and the second direction Y approximately orthogonal to the first direction X, depending on the dimension of the formed product to be manufactured.

(First Corrugating Step)

A first forming die 20 used in a first corrugating step will now be described. As illustrated in FIGS. 4 and 5, an elongate first upper die 21 and an elongate first lower die 25 are provided to extend along the second direction Y. An upper elongate projection 23 is provided on a fixed plate 22 of the first upper die 21 to project downward and a pair of lower elongate projections 27 is provided on the fixed plate 26 of the first lower die 25 to project upward with a space between the lower elongate projections 27 along the first direction X. The upper elongate projection 23 is disposed above a middle portion between a pair of the lower elongate projections 27. When the first upper die 21 is lowered to the lower limit position as illustrated with an imaginary line in FIG. 5, the upper elongate projection 23 is inserted between a pair of the lower elongate projections 27. In a state where the upper elongate projection 23 is lowered to be inserted between a pair of the lower elongate projections 27, there is a gap C1 between the upper elongate projection 23 and each of the lower elongate projections 27. The gap C1 has a dimension corresponding to the thickness t of the raw metal plate 15 plus 0.1 mm.

A distance W1 between a pair of the lower elongate projections 27 in the first direction X is same as the pitch λ1 of the first corrugated portion 11. A distance d1 is the vertical distance between the lower end of the upper elongate projection 23 and the upper end of the lower elongate projection 27 in a state where the first upper die 21 is lowered to the lower limit position. A half-height A1 is half the height of the first corrugated portion 11. The distance d1, the half-height A1, and the thickness t are each set to satisfy d1=2×(A1−t). The distance d1 takes a negative value when the lower end of the upper elongate projection 23 is positioned above the upper end of the lower elongate projection 27 and takes a positive value when the lower end of the upper elongate projection 23 is positioned below the upper end of the lower elongate projection 27.

Specifically, the half-height A1 of the first corrugated portion 11 is set to 0.22 mm to 1.25 mm, the pitch λ1 of the first corrugated portion 11 is set to 2 mm to 2.8 mm, the distance d1 is set to −0.56 mm to +1.5 mm, and the distance W1 is set to 2 mm to 2.8 mm.

When forming the first corrugated portion 11 with the first forming die 20, as illustrated in FIGS. 4 and 5, the raw metal plate 15 is set approximately horizontal in a feeding device (not shown) so that the first direction X of the raw metal plate 15 is a feed direction F1 to the first forming die 20. The feeding device feeds the raw metal plate 15 in the feed direction F1 by a takt-drive with a pitch corresponding to the distance W1 between a pair of the lower elongate projections 27, and thus the raw metal plate 15 is fed between the first upper die 21 and the first lower die 25 of the first forming die 20. On completion of each feed by the takt-drive, the first upper die 21 is lowered to the lower limit position illustrated with the imaginary line in FIG. 5 to die-press the raw metal plate 15 using the upper elongate projection 23 and a pair of lower elongate projections 27, thereby forming one corrugation that constitutes a part of the first corrugated portion 11, and then the first upper die 21 is moved upward to separate the upper elongate projection 23 away from the raw metal plate 15. This step of die-pressing is repeated to form the first corrugated portions 11 on the entire raw metal plate 15, and thus the primary formed plate 16 is manufactured.

Instead of the first lower die 25, a flat plate-shaped first lower die 25A having a slit 27A of the same width as the gap between the faces of a pair of the lower elongate projections 27, which oppose to each other, as illustrated in FIG. 13 may be used. Furthermore, the first corrugated portion 11, which has a smaller half-height than those of the second corrugated portion 12 and the third corrugated portion 13 which will be described later, can be formed using first forming die 20B including a pair of gear-shaped corrugating rolls 28 and 29 instead of the first forming die 20 as illustrated in FIG. 14, where the raw metal plate 15 is passed between a pair of the gear-shaped corrugating rolls 28 and 29.

(Second Corrugating Step)

A second forming die 30 used in a second corrugating step will now be described. As illustrated in FIGS. 6 and 7, an elongate second upper die 31 and an elongate second lower die 35 are provided to extend along the first direction X. An upper elongate projection 33 is provided on a fixed plate 32 of the second upper die 31 to project downward and a pair of lower elongate projections 37 is provided on a fixed plate 36 of the second lower die 35 to project upward with a space between the lower elongate projections 37 along the second direction Y. The upper elongate projection 33 is disposed above a middle portion between a pair of the lower elongate projections 37. When the second upper die 31 is lowered to the lower limit position as illustrated with an imaginary line in FIG. 7, the upper elongate projection 33 is inserted between a pair of the lower elongate projections 37. In a state where the upper elongate projection 33 is lowered to be inserted between a pair of the lower elongate projections 37, there is a gap C2 between the upper elongate projection 33 and the lower elongate projection 37. The gap C2 has a dimension corresponding to the thickness t1 of the primary formed plate 16 plus 0.1 mm.

A distance W2 between a pair of the lower elongate projections 37 in the second direction Y is same as the pitch λ2 of the second corrugated portion 12.

The half-height A2 of the second corrugated portion 12 is two to four times the half-height A1 of the first corrugated portion 11. The pitch λ2 of the second corrugated portion 12 is 2.14 to 5.5 times the pitch λ1 of the first corrugated portion 11. A distance d2 is the vertical distance between the lower end of the upper elongate projection 33 and the upper end of the lower elongate projection 37 in a state where the second upper die 31 is lowered to the lower limit position. The distance d2 is set so that the half-height A2 is within the value range.

When the second corrugated portion 12 is formed with the second forming die 30, as illustrated in FIGS. 6 and 7, the primary formed plate 16 is set approximately horizontal in a feeding device (not shown) so as the second direction Y of the primary formed plate 16 to be in a feed direction F2 to the second forming die 30. The feeding device feeds the primary formed plate 16 in the feed direction F2 by a takt-drive with a pitch corresponding to the distance W2 between a pair of the lower elongate projections 37, and thus the primary formed plate 16 is fed between the second upper die 31 and the second lower die 35 of the second forming die 30. On completion of each feed by the takt-drive, the second upper die 31 is lowered to the lower limit position illustrated with the imaginary line in FIG. 7 to die-press the primary formed plate 16 using the upper elongate projection 33 and a pair of the lower elongate projections 37, thereby forming one corrugation that constitutes a part of the second corrugated portion 12, and then the second upper die 31 is moved upward to separate the upper elongate projection 33 away from the primary formed plate 16. This step of die-pressing is repeated to form the second corrugated portions 12 on the entire primary formed plate 16, and thus the secondary formed plate 17 is manufactured.

Similarly to the first lower die 25A illustrated in FIG. 13, a flat plate-shaped second lower die having a slit of the same width as the gap between the faces a pair of the lower elongate projections 37, which oppose to each other, may be used instead of the second lower die 35. In addition, the second corrugated portions 12 each having a larger half-height than that of the first corrugated portion 11 can be die-pressed to have depth increasing stepwise. Specifically, as in the second forming die 30A illustrated in FIG. 15, there may be provided a second lower die 35A that has three or more lower elongate projections 37 provided in parallel and a second upper die 31A that has a plurality of upper elongate projections 33A each corresponding to a gap between adjacent lower elongate projections 37, where the upper elongate projections 33A individually have bottom ends whose positions go down as the upper elongate projections 33A are close to the forward side of the takt-drive. With such a configuration, die-pressing with the depth increasing in a stepwise manner can be performed. Furthermore, the second corrugated portion 12 needs not be formed approximately orthogonal to the first corrugated portion 11 as described above as long as the second corrugated portion 12 intersects the first corrugated portion 11.

(Third Corrugating Step)

A third forming die 40 used in a third corrugating step will now be described. As illustrated in FIGS. 10 and 11, an elongate third upper die 41 and an elongate third lower die 45 are provided to extend along the second direction Y. An upper elongate projection 43 is provided on a fixed plate 42 of the third upper die 41 to project downward and a pair of lower elongate projections 47 are provided on the fixed plate 46 of the third lower die 45 to project upward with a space between the lower elongate projections 47 along the first direction X. The upper elongate projection 43 is disposed above a middle portion between a pair of the lower elongate projections 47. When the third upper die 41 is lowered to the lower limit position as illustrated with an imaginary line in FIG. 11, the upper elongate projection 43 is inserted between a pair of the lower elongate projections 47. In a state where the upper elongate projection 43 is lowered and inserted between a pair of the lower elongate projections 47, there is a gap C3 between the upper elongate projection 43 and the lower elongate projection 47. The gap C3 has a dimension corresponding to the thickness t2 of the secondary formed plate 17 plus 0.1 mm.

A distance W3 between a pair of the lower elongate projections 47 in the first direction X is same as the pitch λ3 of the third corrugated portion 13. The thickness t2 of the secondary formed plate 17 is set to t2=A2×2.

Specifically, the half-height A3 of the third corrugated portion 13 is two to four times the half-height A1 of the first corrugated portion 11. The pitch λ3 of the third corrugated portion 13 is 2.14 to 5.5 times the pitch λ1 of the first corrugated portion 11. A distance d3 is the vertical distance between the lower end of the upper elongate projection 43 and the upper end of the lower elongate projection 47 in a state where the third upper die 41 is lowered to the lower limit position. The distance d3 is set so that the half-height A3 is within the value range. The half-height A3 and the pitch λ3 of the third corrugated portion 13 may be set respectively same as the half-height A2 and the pitch λ2 of the second corrugated portion 12 or to different values.

When the third corrugated portion 13 is formed with the third forming die 40, as illustrated in FIGS. 10 and 11, the secondary formed plate 17 is set approximately horizontal in a feeding device (not shown) so that the first direction X of the secondary formed plate 17 is a feed direction F3 to the third forming die 40. The feeding device feeds the secondary formed plate 17 in the feed direction F3 by a takt-drive with a pitch corresponding to the distance W3 between a pair of the lower elongate projections 47, and thus the secondary formed plate 17 is fed between the third upper die 41 and the third lower die 45 of the third forming die 40. On completion of each feed by the takt-drive, the third upper die 41 is lowered to the lower limit position illustrated with the imaginary line in FIG. 11 to die-press the secondary formed plate 17 using the upper elongate projection 43 and a pair of the lower elongate projections 47, thereby forming one corrugation that constitutes a part of the third corrugated portion 13, and then the third upper die 41 is moved upward to separate the upper elongate projection 43 away from the secondary formed plate 17. This step of die-pressing is repeated to form the third corrugated portions 13 on the entire secondary formed plate 17, and thus the metal embossed plate 10 is manufactured.

The third forming die 40 may be omitted by effectively using the second forming die 30 also as a third forming die. In this case, the third corrugated portion 13 is formed by feeding the secondary formed plate 17 to the second forming die 30 by a takt-drive so that the first direction X of the secondary formed plate 17 is the feed direction F2 of the second forming die 30. Similarly to the first lower die 25A illustrated in FIG. 13, a flat plate-shaped third lower die having a slit of the same width as the gap between the faces of a pair of lower elongate projections 47, which oppose to each other, may be used instead of the third lower die 45. Furthermore, since the half-height of the third corrugated portion 13 is larger than that of the first corrugated portion 11, the third forming die like the second forming die 30A illustrated in FIG. 15 may be used to form a corrugated portion.

In this manufacturing method, the raw metal plate is die-pressed using the upper elongate projection 23 and the lower elongate projection 27 to sequentially form the first corrugated portions 11, the primary formed plate 16 is die-pressed using the upper elongate projection 33 and the lower elongate projection 37 to sequentially form the second corrugated portions 12, and the secondary formed plate 17 is die-pressed using the upper elongate projection 43 and the lower elongate projection 47 to sequentially form the third corrugated portions 13. In such a manner, the corrugated portions are formed on the raw metal plate 15 without causing a large tensile stress. The rigidity of the metal embossed plate 10 can be improved by increasing the total thickness of the metal embossed plate 10 while minimizing the residual strain throughout the metal embossed plate 10. Accordingly, a metal embossed plate 10 having high rigidity can be obtained from a very thin raw metal plate 15. In addition, the range of designing a product that can be formed by deep-drawing can be broadened, since the second corrugated portion 12 and the third corrugated portion 13 that have large half-heights can be formed on the metal embossed plate 10 with large elongation percentages in the first direction X and the second direction Y. Therefore, not just only an aluminum alloy plate but a stainless steel plate can be deep-drawn without difficulty, and a covering member 51 having a shape suitably fit to the shape of an exhaust part member of a road vehicle, such as the exhaust manifold 50, can easily be manufactured without difficulty.

Although the embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above. It goes without saying that the embodiments can be changed without departing from the spirit and the scope of the present invention. 

What is claimed is:
 1. A method of manufacturing a metal embossed plate comprising: sequentially forming a plurality of first corrugated portions in a first direction by die-pressing a raw metal plate; sequentially forming a plurality of second corrugated portions in a second direction intersecting the first direction by die-pressing a primary formed plate having the first corrugated portions, each of the plurality of second corrugated portions having a half-height and a pitch larger than a half-height and a pitch of each of the first corrugated portions, and the die-pressing being performed using an elongate projection provided on at least one of a pair of dies capable of approaching and separating from each other; and sequentially forming a plurality of third corrugated portions approximately in the first direction by die-pressing a secondary formed plate having the second corrugated portions, each of the plurality of third corrugated portions having a half-height and a pitch larger than the half-height and the pitch of the first corrugated portion, the die-pressing being performed using an elongate projection provided on at least one of a pair of dies capable of approaching and separating from each other.
 2. The method of manufacturing a metal embossed plate according to claim 1, wherein the first direction and the second direction are approximately orthogonal.
 3. The method of manufacturing a metal embossed plate according to claim 1, wherein the half-height and the pitch of the second corrugated portion are set approximately same as the half-height and the pitch of the third corrugated portion, respectively.
 4. The method of manufacturing a metal embossed plate according to claim 1, wherein the half-height of the third corrugated portion is 2 to 4 times the half-height of the first corrugated portion, and the pitch of the third corrugated portion is 2.14 to 5.5 times the pitch of the first corrugated portion.
 5. The method of manufacturing a metal embossed plate according to claim 1, wherein a stainless steel plate is used as the raw metal plate.
 6. The method of manufacturing a metal embossed plate according to claim 1, wherein any one of the first corrugated portion, the second corrugated portion, and the third corrugated portion is die-pressed by a forming die having a surface that is treated with surface treatment by which dry lubricity of the surface increases.
 7. The method of manufacturing a metal embossed plate according to claim 1, wherein the first corrugated portions are sequentially formed by die-pressing with a pair of gear-shaped corrugating rolls.
 8. The method of manufacturing a metal embossed plate according to claim 1, wherein at least one of the second corrugated portion and the third corrugated portion is die-pressed multiple times to have depth that increases in a stepwise manner.
 9. The method of manufacturing a metal embossed plate according to claim 1, wherein only three types of corrugated portions which are the first corrugated portion, the second corrugated portion, and the third corrugated portion are sequentially formed on the raw metal plate. 